Manual sealers provide positive sealing action with minimal effort. They interlock overlapping courses of a strap into a high strength joint. One type of sealing tool is a manual notch-type sealer that cuts into and seals the outer edges of the strap, turning tabs down (down notch) or up (reverse notch). Crimp-type sealers press the edges of the strap and the seal into wavy crimps especially shaped to produce maximum frictional forces on the strap.
There are two principal types of manual strap sealers, front action sealers and side action sealers. Front-action sealer handles are held perpendicular to the strap, usually in front of the operator who forces the handles together for maximum leverage. These are generally used for light duty strap applications. Side-action sealers have a lower handle that can be rested on the flat surface of the load being strapped. Operators can apply much of their weight, again for maximum leverage, with both hands on the upper handle. These are generally used in heavier strap applications.
The joint is the weakest part of the system, therefore the type of joining method used is very important if strength is an issue. The strength of a joint is defined as the force required to break the strap in uniaxial tension. This is then compared to the uniaxial strength of the strap and recorded as the percent difference (e.g., a sample of strap may have a 5,000 lb (2,300 kg) break strength and the seal may fail at 3,750 lbs. (1,750 kg), so the seal is said to have a 75% strength). Hot knife welds have a minimum break strength of 55%. Friction welds have a minimum break strength of 65%.